The cysteine containing phosphoproteins (CCPs) are a family of salivary proteins whose members are found in in vitro pellicle and may be cysteine protease inhibitors (cystatins). A non-salivary cystatin bearing 60% homology with salivary cystatin S has been reported to have in vitro anti-viral activity. Our efforts are focussed on describing the heterogeneity of the CCPs and what impact this may have on their function(s) in the oral cavity. Following purification of a phosphorylated CCP and a non- phosphorylated CCP and determination of the sequence and covalent structure of each of these CCPs, we will compare the function of each CCP with regard to cysteine protease inhibitory activity, possible calcium binding activity, and the effect of apatite binding on these other two functions. The purified proteins will be used to develop antisera specific for the phosphorylated and non-phosphorylated CCPs. Synthesized CCP peptides may be required for specific-antibody production. The antisera will be additional tools for the research described above and will be used for the localization of these various CCPs in pellicles and mucous coats in vivo. We hope to expand our future efforts to include both an investigation of possible anti- viral activity and a description of the cellular processing of this excretory phosphoprotein.